Display technologies being developed by the assignee, and others, are able to reproduce images having high dynamic range (HDR). Such displays can reproduce images that more faithfully represent real-world scenes than conventional displays.
To support backwards compatibility as well as new HDR display technologies, an HDR image may be represented by a tone-mapped image with additional metadata comprising grayscale luminance ratios. On one hand, the tone-mapped image may be used to present a normal dynamic range image (e.g., on a legacy display). On the other hand, the additional metadata may be used with the tone-mapped image to generate, recover, or present an HDR image (e.g., by an HDR display).
However, a tone-mapped image may comprise one or more color alterations caused for various reasons in connection with a user who is manipulating the image or with a particular tone mapping operator used to generate the tone-mapped image. For example, the user may change hue information related to some or all of the pixels in the image in order to create a more artistic looking image. In addition, a tone-mapping operator may perform different black or white clippings in various color channels, and may introduce color alterations, for example, in relatively underexposed or overexposed regions of the image. Under existing techniques, these color alterations in the tone-mapped image are difficult or impossible to remove when a downstream decoder tries to reconstruct an HDR image from a tone-mapped image and accompanying grayscale luminance ratios.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.